Deformation conditions and quartz c-axis fabric development along nappe boundaries: The Andrelândia Nappe System, Southern Brasília Orogen (Brazil)

The Liberdade and Andrelândia nappes, SE Brazil, record the western Gondwana amalgamation in the Southern Brasília Orogen during the Ediacaran. The Liberdade Shear Zone acted as the boundary between these two overlapping nappes. Quartz c-axis fabrics and strain data from quartzite samples and petrol...

Full description

Saved in:
Bibliographic Details
Published in:Tectonophysics 2019-09, Vol.766, p.283-301
Main Authors: Rodrigues, Sérgio Wilians de Oliveira, Martins-Ferreira, Marco Antonio Caçador, Faleiros, Frederico Meira, Campos Neto, Mário da Costa, Yogi, Maria Thereza Akemi Guimarães
Format: Article
Language:English
Subjects:
Andrelândia nappe
Biotite
Boundary conditions
C-axis fabrics
Constraint modelling
Deformation
Fabrics
Garnet
Gondwana
Grain boundary migration
Liberdade Shear Zone
Mica
Muscovite
Nappes
Opening angles
Orogeny
Phase diagrams
Pressure data
Pressure effects
Quartz
Quartz CPO
Quartzite
Recording
Recrystallization
Schist
Schists
Shear zone
Sillimanite
Tectonic processes
Tectonics
Temperature
Temperature effects
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The Liberdade and Andrelândia nappes, SE Brazil, record the western Gondwana amalgamation in the Southern Brasília Orogen during the Ediacaran. The Liberdade Shear Zone acted as the boundary between these two overlapping nappes. Quartz c-axis fabrics and strain data from quartzite samples and petrological data from hosting metapelite rocks were analyzed to investigate the tectonic processes involved in nappe development. Further constraints were achieved by conducting petrological modeling and geothermobarometry using P–T isochemical phase diagram approaches. Quartz axis plots show consistency with different kinematic criteria verified in the field in meso and macroscale. The fabrics are associated to both coaxial deformation and non-coaxial deformation. Quartz microstructures, metamorphic assemblages and c-axis concentrations primarily around Y and X structural directions suggest that deformation was accommodated by grain boundary migration recrystallization under temperature above 500 °C. Disregarding pressure effects the opening angles of quartz c-axis fabrics suggest temperatures between 480 and 640 °C (muscovite quartzite) and 650–720 °C (sillimanite quartzite). Considering pressure data, the opening angles indicate conditions of 550–650 °C and 7–10 kbar (muscovite quartzite) and 600–730 °C and 4–7 kbar (sillimanite quartzite), reflecting primarily distinct baric regimes. Sillimanite-bearing samples estimatives are supported by ubiquitous presence of chessboard subgrain patterns in quartz and by modeled isochemical phase diagrams that constrain conditions of 660–730 °C and 6–7 kbar for garnet-sillimanite-biotite schist samples. Altogether, these results indicate progressive tectonic evolution linked to oblique convergence between tectonic units represented by the Andrelândia and Liberdade nappes and the Paleoproterozoic basement. Besides recording distinct thermal and baric regimes, the nappes also present different structural styles, suggesting that pressure and temperature are important boundary conditions for the nappe structural style. •C-axis and aperture angles differentiate nappes with different histories.•Lateral extrusion explains oblique plunging lines and metamorphic variation.•The Liberdade Shear Zone has a transpressive character.•OA and paragenesis indicate P-T conditions of 500–710 °C and 4–10 kbar.•Thermobarometry and petrological modeling constrain 660–730 °C and 6–7 kbar.
ISSN:0040-1951
1879-3266
DOI:10.1016/j.tecto.2019.06.014